A radar device using an FMCW (Frequency Modulated Continuous Wave) signal receives the FMCW signal transmitted from a transmitter and reflected by an object, and multiplies the reception signal by a transmission signal transmitted at the reception time. Here, the output frequency of the multiplier is decided by the time difference between the signals, so that the distance to the object, the relative speed and so on can be obtained.
The FMCW signal for a radar is required to have characteristics that its frequency almost linearly varies with respect to time. There is a conventionally known method in which the frequency of the output signal from a voltage-controlled oscillator is converted into voltage and compared with a voltage signal in a triangular wave shape inputted from an external part, and the error (difference) between them is used to obtain high linearity. There is another known method in which the sensitivity of the voltage-controlled oscillator converting voltage into frequency is measured using a phase synchronization circuit and a variable frequency divider, a signal with the non-linearity of the voltage-controlled oscillator corrected based on the sensitivity is generated, and the voltage-controlled oscillator is controlled by the correction signal with the phase synchronization circuit opened, to generate the FMCW signal with high linearity. There is still another known method in which the frequency of a reference signal in a triangular wave is multiplied using a phase synchronization circuit with a narrow loop bandwidth, and the multiplied signal is used as a reference signal for a phase synchronization circuit with a wide loop bandwidth.